History of bacterial ring rot of potato in the Czech Lands and a proposal for relaxation of strict quarantine measures

In the supposed or proven incidence of bacterial ring rot caused by Clavibacter michiganensis subsp. sepedonicus (Cms) in certified seed and commercial potatoes, five periods can be identified in the Czech Lands from 1910 to 2006: (i) high incidence of Cms in potato crops is claimed (about 1910-1929); (ii) very low incidence in certified potatoes and sporadic occurrence in commercial potatoes (about 1930-1985); (iii) increasing incidence of Cms in certified seed potatoes and its sporadic occurrence in commercial potatoes is assumed (about 1986-1997); (iv) a relatively high percentage of potato tuber samples proved to be infected by Cms, namely 1.14% in seed potatoes in 1998 and 4.13% in commercial potatoes in 1999 (1998-2004 period); (v) progressive decrease of Cms incidence to zero in seed potato samples and 0.19% in commercial samples in 2005, followed by a slight increase to 0.15% in seed potatoes and 0.23% in commercial potatoes in 2006 (2005-2006 period). Thus, up to 2006, Cms was and is not widely distributed in the CR and is actively and effectively controlled, mainly through the zero tolerance for ring rot bacterium in the seed potato certification program. In the CR, Cms has a relatively low capacity for damage and can hardly be considered as a pest of national economic importance. Strictly speaking, Cms does not fulfill the criteria for a quarantine organism. If, however, the quarantine status of Cms will be maintained, the severe post-entry measures against it should be relaxed.